Fine particles have a great ratio of the surface area to the volume thereof, and they generally behave in a different manner from materials having small ratio of the surface area to the volume. For example, fine particles of inorganic materials such as titanium oxide, zinc oxide and the like have eliminating action of ultraviolet ray, antibacterial action, catalytic action and the like.
Among fine particles of inorganic materials, fine particles having a diameter in a nanometer size (superfine particles) are expected to exhibit a quantum effect. Accordingly, industrial utilization of the fine particles has drawn attention. In particular, in respect of superfine particles having the diameter in nanometer size, there is an urgent need to develop industrial manufacturing techniques of elements utilizing the quantum effects.
Protein fine particles having the diameter of about 10 to 20 nm have drawn attention in regard to utilization for biosensors and the like. Particularly, among various protein fine particles, there exist fine particles capable of including inorganic materials inside. Such protein fine particles have both features of fine particles of the inorganic materials as described above and of fine particles of a protein.
The fine particles described hereinabove usually have distributed in the form of a colloidal solution. However, it is disadvantageous in efficient utilization of the fine particle functions in the colloidal solution as it is. Therefore, techniques which allow industrially efficient utilization of the functions of fine particles have been sought in which the aforementioned colloidal solution is utilized as a raw material.
Conventionally, two-dimensional crystal films comprising protein fine particles have been utilized in crystal structure analyses of a protein by an electron microscope. In this analysis, a two-dimensional crystal film comprising the protein fine particles is produced by filling a colloidal solution of the protein fine particles in a trough, and concentrating the protein fine particles on a gas-liquid interface of this colloidal solution. According to this process, because the two-dimensional crystal film is formed on the gas-liquid interface, the two-dimensional crystal film is liable to be disrupted through vibration.
Thus, as a technique which can be industrially utilized in an efficient manner, methods to arrange fine particles on a substrate have been believed to be most efficient. Therefore, to establish techniques for readily forming an ideal fine particle film on a substrate with fine particles being regularly arranged at a high density has been desired.
As a technique for arranging protein fine particles on a substrate developed heretofore, a transfer method developed by Yoshimura et al. (Adv. Biophys., Vol. 34, p99-107 (1997)) is explained below with reference to FIG. 12.
First, in the step shown in FIG. 12 (a), a liquid 24 with protein fine particles 45 dispersed therein is injected into a sucrose solution 23 having the concentration of 2% using a syringe 25.
Next, in the step shown in FIG. 12 (b), the liquid 24 is elevated up to the surface of the sucrose solution 23.
Next, in the step shown in FIG. 12 (c), the liquid 24 reached to the gas-liquid interface first forms an amorphous film 26 of the protein fine particles, and the protein fine particles 45 reached afterwards come to attach beneath the amorphous film 26.
Next, in the step shown in FIG. 12 (d), a two-dimensional crystal film 27 of the fine protein fine particles 45 is formed beneath the amorphous film 26. Then, as is illustrated in FIG. 12 (d), on a film 28 including the amorphous film 26 and the two-dimensional crystal film 27 of the protein fine particles 45, disposed a substrate 21 (silicon wafer, carbon grid, glass substrate or the like), thereby transferring the film 28 to the surface of the substrate 21.
However, according to the aforementioned conventional method, it is highly possible that a breakage of the film 28 occurs in the step shown in FIG. 12 (d), and it is also highly possible that a part of the protein fine particles of the two-dimensional crystal film 27 may fall away upon the transfer. Accordingly, there are problems involving difficulties in transferring a two-dimensional crystal film having a great area to a substrate without failure.
Therefore, according to the aforementioned method of Yoshimura et al., there is disclosed a method to accelerate the transfer of protein fine particles onto a substrate surface by treating the substrate surface with aminopropylmethoxy silane so that the substrate surface is positively charged at pH of around 7, in instances where the protein has negative charge at pH of around 7. In addition, it has been also revealed that protein fine particles are liable to bind with each other.
However, when the state of transfer of the protein fine particles to the substrate in the two-dimensional crystal film which was obtained according to the method described above is observed, with SEM or AFM, directions of symmetric axes of the protein fine particles are revealed to be random. Such random directionality results from the sites being random where the protein fine particles contact with the substrate in the method described above. Therefore, according to the method described above, protein fine particles may form a comparatively aggregated structure, however, it is difficult to obtain a two-dimensional crystal film having protein fine particles arranged at a high density in a highly accurate and regular manner, with directions of the symmetric axes of the protein fine particles being coordinated. In other words, directional control of the crystal axis of the two-dimensional crystal film is extremely difficult.